In recent years, it has been being made known that bubbles with small diameters have various effects. Currently, advances are being made in studies on techniques for preparing such bubbles and their effects. Moreover, attempts are being made to degrade various types of organic matter with use of bubbles.
The bubbles can be classified into microbubbles, micro-nanobubbles, and nanobubbles according to their diameters. Specifically, the microbubbles are bubbles generated with diameters of 10 μm to several tens of micrometers. The micro-nanobubbles are bubbles generated with diameters of several hundreds nanometers to 10 μm. The nanobubbles are bubbles generated with diameters of not more than several hundreds nanometers. It should be noted that the microbubbles change partially into micro-nanobubbles through contraction motions after generation. Further, the nanobubbles have such properties that they can stay in a liquid over a long period of time.
For example, there have conventionally been known various methods for using nanobubbles and various apparatuses using nanobubbles (e.g., see Patent Literature 1 [Japanese Patent Application Publication, Tokukai, No. 2004-121962 A (Publication Date: Apr. 22, 2004)]). More specifically, Patent Literature 1 teaches that nanobubbles exhibit surface action and bactericidal action through an increase in surface area, an enhancement in surface activity, generation of a local high-pressure field, or realization of electrostatic polarization. Furthermore, Patent Literature 1 describes a technique for cleansing various objects and a technique for purifying polluted water with use of the surface action and bactericidal action of the nanobubbles. Furthermore, Patent Literature 1 describes a method for refreshing living organisms with use of the nanobubbles. It should be noted that Patent Literature 1 produces the nanobubbles by electrolyzing water and imparting ultrasonic vibrations to the water.
Further, there has conventionally been known a method for preparing nanobubbles from a liquid (e.g., see Patent Literature 2 [Japanese Patent Application Publication, Tokukai, No. 2003-334548 A (Publication Date: Nov. 25, 2003)]). The preparation method includes the steps of: in a liquid, (1) turning part of the liquid into cracked gas; (2) applying ultrasonic waves to the liquid; or (3) turning part of the liquid into cracked gas and applying ultrasonic waves to the liquid. It should be noted that Patent Literature 2 teaches that it is possible to apply electrolysis or photolysis to the step of turning part of the liquid into cracked gas.
Further, there has conventionally been used a waste liquid treatment apparatus using microbubbles of ozone gas (ozone microbubbles) (e.g., see Patent Literature 3 [Japanese Patent Application Publication, Tokukai, No. 2004-321959 A (Publication Date: Nov. 18, 2004)]). The waste liquid treatment apparatus prepares microbubbles of ozone gas by mixing ozone gas prepared by an ozone generating apparatus into a waste liquid with use of a pressure pump. Moreover, the microbubbles react with organic matter contained in the waste liquid, whereby the organic matter contained in the waste liquid is oxidized and degraded.
Furthermore, in recent years, a nanobubble generating apparatus has been being developed which can generate a large amount of nanobubbles (e.g., see Patent Literature 4 [Japanese Patent No. 4118939 (Publication Date: Jul. 16, 2008)]). This nanobubble generating apparatus makes it possible to apply the large amount of nanobubbles to service water treatment, wastewater treatment, and bathtub treatment, and is expanding in application as far as the field of health and the field of medicine.
As mentioned above, the nanobubbles are expected to be useful in various fields. It is advantageous if an apparatus for producing a nanobubble-containing liquid containing nanobubbles can be manufactured at low cost and in a short period of time. Further, there is a demand for further improvement in method for producing a nanobubble-containing liquid.
Under the circumstances, the conventional nanobubble generating apparatus is not sufficient. There is a strong demand for the development of a nanobubble-containing liquid producing apparatus that can be manufactured at lower cost and in a shorter period of time.